• Smart Structures and Systems
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• v.5 no.4
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• pp.329-344
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• 2009

Ultrasonic chaotic excitations combined with sensor prediction algorithms have shown the ability to identify incipient damage (loss of preload) in a bolted joint. In this study we examine a physical experiment on a single-bolt aluminum lap joint as well as a three-dimensional physics-based simulation designed to model the behavior of guided ultrasonic waves through a similarly configured joint. A multiple bolt frame structure is also experimentally examined. In the physical experiment each signal is imparted to the structure through a macro-fiber composite (MFC) patch on one side of the lap joint and sensed using an equivalent MFC patch on the opposite side of the joint. The model applies the waveform via direct nodal displacement and 'senses' the resulting displacement using an average of the nodal strain over an area equivalent to the MFC patch. A novel statistical classification feature is developed from information theory concepts of cross-prediction and interdependence. This damage detection algorithm is used to evaluate multiple damage levels and locations.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.7
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• pp.2078-2086
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• 1996

This paper introduces two three-dimensional eight-node hexagonal elements obtained by using multivariable variational mehtod. Both of them are based on the modified hellinger-reissner principle to employ incompatible displacements and assumed stresses of assumed strains. The internal functions of element are introduced to as element formulation through two different methods : the first one uses the functions determined directly from the element boundary condition of the incompatible displacements ; while the second, being a kind of B-bar mehtod, employs the modification technique of strain-displacement matrix to pass the patch test. The elements are evaluated on the selective problems of bending and material incompressibility with regular and distorted meshes. The results show that the new elements perform with good accuracy in both of deformation and stress calculation and they are insensitive to distorted geometry of element.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.8
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• pp.834-842
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• 2002

The method of moment is applied to the analysis of electromagnetic scattering from an arbitrarily-shaped conductor. The conducting surface is discretized into triangular patches using a GID tool. Surface currents on a conductor are expanded with a vector triangle basis function. By using the Duffy's method, the singular integration appeared in a triangle patch can be transformed into the non-singular integral form suitable for one dimensional Gaussian quadrature integration method. Mutual and self integration extracted singular terms are evaluated by two dimensional Gaussian quadrature techniques.

• Structural Engineering and Mechanics
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• v.5 no.2
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• pp.137-148
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• 1997

In computing eigenvalues for a large finite element system it has been observed that the eigenvalue extractors produce eigenvectors that are in some sense more accurate than their corresponding eigenvalues. From this observation the paper uses a patch type technique based on the eigenvector for one mesh quality to provide an eigenvalue error indicator. Tests show this indicator to be both accurate and reliable. This technique was first observed by Stephen and Steven for an error estimation for buckling and natural frequency of beams and two dimensional in-plane and out-of-plane structures. This paper produces and error indicator for the more difficult problem of three dimensional brick elements.

• Proceedings of the Korean Society of Rheology Conference
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• 2006.06a
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• pp.81-84
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• 2006

Slot coating process, in continuous and patch modes, has been applied for the many precise coating products, e.g., flat panel displays and second batteries. However, manufacturing uniform coating products is not a trivial task at high-speed operations because various flow instabilities or defects such as leaking, bubbles, ribbing, and rivulets are frequently observed in this process. It is no wonder, therefore, that many efforts to understand the various aspects of dynamics and coating windows of this process have been made both in academia and industry. In this study, as the first topic, flow dynamics within the coating bead in slot coating process has been investigated using the one-dimensional viscocapillary model by lubrication approximation and two-dimensional model by Flow-3D software. Especially, operability windows in both 1D and 2D cases with various slot die lip designs have been successfully portrayed. Also, effects of process conditions like viscosity and coating gap size on slot coating window have been analyzed. Also, some experiments to find minimum coating thickness and coating windows have been conducted using slot die coater implemented with flow visualization device, corroborating the numerical results. As the second topic, flow dynamics of both Newtonian and Non-Newtonian fluids in patch or pattern slot coating process, which is employed in manufacturing IT products such as secondary batteries, has been investigated for the purpose of optimal process designs. As a matter of fact, the flow control in this system is more difficult than in continuous case because od its transient or time-dependent nature. The internal die and die lip designs for patterned uniform coating products have been obtained by controlling flow behaviors of coating liquids issuing from slot. Numerical simulations have been performed using Fluent and Flow-3D packages. Flow behavior and pressure distribution inside the slot die has been compared with various die internal shapes and geometries. In the coating bead region, efforts to reduce irregular coating defects in head and tail parts of one patterned coating unit have been tried by changing die lip shapes. It has been concluded that optimal die internal design gas been developed, guaranteeing uniform velocity distribution of both Newtonian and shear thinning fluids at the die exit. And also optimal die lip design has been established, providing the longer uniform coating layer thickness within one coating unit.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.2
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• pp.192-201
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• 2003

In this paper, to reduce the size of patch, three types of 3-dimensional patch antennas which are one-directionally-corrugaged type, rectangular ring-likely corrugated type, and lattice-likely corrugated type rectangular microstrip patch antennas(MPA) are designed and fabricated at the 1.575 GHz. As the result, one-directionally corrugated rectangular MPA is reduced in the resonant length of patch by 21.4% than that of general plane MPA. -10 dB bandwidth(B.W) is 62 MHz(3.9 %) and this is broader than that(39 MHz, 2.5 %) of plane MPA by 23 MHz(1.5 %). The gain is 5.8 dBd and this is reduced by 0.9 dB than that(6.7 dBd) of plane MPA. Half power beamwidth(HPBW) is broadened by 18$^{\circ}$ than that of plane MPA in the E-plane and this is due to the reduced length of patch. For rectangular ring-likely corrugated retangular MPA, the patch size is miniaturized by 21.6 % than that of plane MPA. For lattice-likely corrugated rectangular MPA, in the linear polarization, the size of patch is miniaturized by 43.3 % than that of plane MPA. -10 dB B.W is 70 MHz(4.4 %) and this is broadened than that of plane MPA by 31 MHz(2 %). Gain is 2.2 dBd and this is smaller than that of plane MPA by 4.5 dB. HPBW is increased in both E-plane and H-plane by 22$^{\circ}$ and 13$^{\circ}$, respectively. For circular polarization, the size of patch is reduced by 41 % than that by 41 %. The axial ratio(AR) is 0.8 dB at the 1.575 GHz and the axial ratio bandwidth(ARBW) within 2 dB is 20 MHz(1.27 %) and this is increased by 10 MHz(0.63 %) than that 10 MHz(0.63 %) of plane MPA. From all the results above, it is conformed that the proposed antenna has merit in size reduction of patch and in the input impedance B.W, and is more profitable in many application than the general plane type MPA.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.292-297
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• 2001

Composite patch repair of cracked aircraft structures has been accepted as one of improving fatigue life and attaining better structural integrity. Analysis for the stress intensity factor at the skin/stiffener structure with inclined central crack repaired by composite stiffened panels are developed. A numerical investigation was conducted to characterize the fracture behavior and crack growth behavior. In order to investigate the crack growth direction, maximum tangential stress(MTS) criteria is used. The main objective of this research is the validation of the inclined crack patching design. In this paper, the reduction of stress intensity factors at the crack-tip and prediction of crack growth direction are determined to evaluate the effects of various non-dimensional design parameter including; composite patch thickness and stiffener distance. The research on cracked structure subjected to mixed mode loading is accomplished and it is evident that more work using different approaches is necessary.

• Composites Research
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• v.29 no.3
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• pp.117-124
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• 2016

The failure strength of composite single-lap joint repaired using scarf patch was investigated by test and finite element method. A total of 45 specimens were tested changing scarf ratio, stacking pattern, and defect size to study the failure strength and mode. Except for one case, all repaired specimens showed the equal or higher strength than the sound specimens and the effect of considered repair parameters was not remarkable. It was found through the failure mode inspection that the surface treatment for bonding was not enough in the case which failed at the lower load than the sound specimen. Three-dimensional finite element analysis was conducted to verify the test results. It was confirmed that the considered repair parameters do not significantly affect the stress distribution of the specimens. It was also observed that the applied tensile load is relieved passing through the overlapped region thickness of which is almost double. From this study, it is concluded that if the bonding procedure for adherends and patch including surface treatment for fabric layer is thoroughly followed, the strength of repaired single-lap joint can be restored up to the strength of sound one.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2000.11a
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• pp.117-120
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• 2000

When analyzing the scatting problem of multi-layered structures using closed-form Green's function, one of the main difficulties is that the numerical integrations for the evaluation of diagonal matrix elements converge slowly and are not so stable. Accordingly, even when the integration for the singularity of type e$\^$-jkr//${\gamma}$/, corresponding to the source dipole itself, is performed using such a mathod, this difficulty persists in the integration corresponding to the finite number of complex images. In order to resolve this difficulty, a new technique based upon the Gaussian quadrature in polar coordinates for the evaluation of the two-dimensional generalized exponential integral is presented. Stability of the algorithm and convergence is discussed. Performance is demonstrated for the example of a microstrip patch antenna.

• Structural Engineering and Mechanics
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• v.8 no.1
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• pp.1-18
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• 1999

Procedures are investigated by which nonlinear finite element shell analysis algorithms can be simplified to provide more cost effective approximate analyses of orthogonally-reinforced concrete flat plate structures. Two alternative effective stiffness formulations, and an unbalanced force formulation, are described. These are then implemented into a nonlinear shell analysis algorithm. Nonlinear geometry, three-dimensional layered stress analyses, and other general formulations are bypassed to reduce the computational burden. In application to standard patch test problems, these simplified approximate analysis procedures are shown to provide reasonable accuracy while significantly reducing the computational effort. Corroboration studies using various simple and complex test specimens provide an indication of the relative accuracy of the constitutive models utilized. The studies also point to the limitations of the approximate formulations, and identify situations where one should revert back to full nonlinear shell analyses.